1. Field of the Invention
The present invention generally relates to an indexable insert drill and, more particularly, is concerned with an indexable drill for producing a hole in a single metal workpiece or a stack of metal workpieces.
2. Description of the Prior Art
Indexable drills are known in the prior patent art. They utilize indexable and replaceable cutting inserts capable of higher surface speeds than conventional steel twist drill. Also, they eliminate the costly grinding to sharpen the cutting end and removal of the tool from the drill. Even though indexable drills have proven to create holes faster and more economically than conventional drills, they still have certain shortcomings which limit their applications. Conventional drills are still widely used throughout the industry in many applications.
One shortcoming of current indexable drills is that they require more rigidity in the part setup and machine spindle than conventional twist drills. Indexable drill geometry is usually of a more unbalanced cutting condition at the point of part entry and during the drill cycle than a conventional center cutting drill which has two equal cutting flutes. Once started in a hole, a conventional drill can be used successfully at great length to diameter ratios. Indexable drill performance severely degenerates as the length to diameter ratios exceed three times diameter.
Another shortcoming of current indexable drills is that they generate a rough hole finish in most material. "Rough" is the term used to compare the surface finish achieved by drills in comparison to the surface finish that can be achieved in the same hole by boring after drilling. Depending on the functional application of the hole, often subsequent machining operations are performed to achieve size and finish after drilling. One common practice with an indexable drill is to "backbore" after drilling by detenting the drill in the axis aligned with the outer insert and reverse feeding the drill back out of the hole. The much better surface finish obtained by this practice clearly demonstrates that the outside insert corner radius is subjected to much more movement in the drilling cycle than the boring cycle.
Still another shortcoming of current indexable drills is that they are considered to be of the rough hole drilling nature. Thus, some allowance is made for manufacturing tolerance in machining the insert pocket and insert size control. The end-user has responsibility to provide the best possible machining conditions. Much size control is lost due to drill "walking" during the cut.
Yet another shortcoming of current indexable drills is chip control. Chip control is very important to drill longevity. Many end users cannot use this type drill due to their inability to provide sufficient amounts of coolant from the machine source. The coolant's primary function is to flush out the chip from the flutes to prevent the re-cutting of chips and to prevent chips from wedging between the outside drill body and the hole inside surface. This condition causes galling of the drill and part surfaces and will destroy the drill.
And another shortcoming of current indexable drills is that the slug created by the drill geometry during cutting prohibits cutting stacked material. The slug will begin to spin with the drill at the parting line of the stacked material and cannot be cut out of the way. The rotating slug will then jam the cutting inserts and cause drill destruction.
A further shortcoming of current indexable drills is horsepower requirements. They require more horsepower from machine tools to cut than do the conventional steel twist drills.
Consequently, a need still exists for improvement of indexable drills so as to overcome these shortcomings without introducing new ones in their place.